The University of Colorado Reproductive Medicine Unit (UC-RMU) is uniquely positioned to be an active and valuable participant in the Cooperative Multi-Center Reproductive Medicine Network of the NICHD. This proposal is jointly submitted by the Sections of Reproductive Endocrinology (Dept. of Obstetrics & Gynecology) and Urology (Department of Surgery). The strengths of this application include: 1) a 16 year history of close and integrated collaboration between the Principal Investigator (reproductive endocrinologist) and Co-Investigator (infertility urologist) in the diagnosis and treatment of infertility patients, 2) specially designed and physically contiguous clinical offices including shared reproductive laboratories, 3) outstanding experience in protocol development, and an extensive and highly successful record as effective contributors to many large multicenter trials including the NICHD Clinical Contraceptive Trials Network since 1996 and the existing Reproductive Medicine Network (RMN) since 2000, 4) a record of excellent patient outcomes and broad referral support from both University and community practitioners, and 5) significant departmental and institutional strengths, the support of numerous complementary clinical services and associated basic scientists, and outstanding resources. The geographic and population diversity represented by our location as one of the very few academic reproductive medicine centers in the Rocky Mountain region is an additional important asset that the UC-RMU brings to the RMN. Our application describes these strengths in detail, and illustrates the close and productive working relationship of reproductive endocrinology and urology with our Concept Protocol entitled A Prospective, Randomized, Placebo-Controlled, Double-Blind Study of Clomiphene Citrate Treatment of Infertile Men with Non-Obstructive Azoospermia. The goal of the RMN is to design and conduct clinical studies investigating problems in reproductive medicine, particularly those that impact fertility, and to facilitate resolution of these problems through a scientifically rigorous network of clinical research units. Individuals with reproductive diseases, infertile couples, and their health care providers will profit by this research. The public health will be enhanced by the birth of healthy, wanted babies, and by better understanding and treatment of conditions in both men and women that produce significant morbidity beyond their effects on fertility.